The over-all objective of this research is to study the effects of undernutrition of neonatal onset on the growth and maturation of the spinal cord. This undernourished state will be achieved by transferring rat pups born of a normal dam to a dam maintained on a diet restricted in quantity by 25% or 50%. The laboratory rat has been selected because of the immature status of its nervous system at birth and throughout the preweaning period. The pups suckled by restricted dams will be compared with their littermates suckled by their natural or foster dams, both of which will be normally nourished. Gross aspects of spinal cord development will be studied at first, with subsequent concentration on the neuroglial population and its proliferative capacities. The latter studies will be carried out by light microscopic autoradiography.